The present invention relates to insulated gate field effect transistors (IGFETs) and, more particularly, to a method for the manufacture of IGFETs having a high speed of response in high density integrated circuits.
In order to obtain high response speeds and high integration densities, either the horizontal dimensions or the vertical dimensions of the IGFETs have to be reduced ("scaling principle"), It is, in particular, necessary to reduce the depth of the source and drain junctions in the substrate. In conventional, commercially available, IGFETs, the use of very thin junctions has, however, produced detrimental results. This, in effect, increases the layer resistance of the active source and drain regions and decreases the reliability of the contact between these regions and their associated electrodes.
In order to counter the above drawbacks, it has been proposed to construct IGFETs having their active source and drain regions formed on the surface of the substrate, rather than inside the substrate. A structure of this type is disclosed, for example, in the U.K. Patent Specification 1,477,083. However, the method used to obtain this structure, as described in this Patent, are very complex and are not compatible with industrial production requirements.
The object of the present invention is to provide an IGFET having ultra-thin junctions, low layer resistances and extremely reliable contacts, by means of a method which is both simple to carry out and involves a sequence of operations compatible with conventional industrial production processes.
This object is achieved by the method described and set out in the attached claims, and illustrated by way of non-limiting example with reference to the attached drawings.